#include "Train.h"

class Solution {
public:
    int waysToStep(int n) {
        if (n <= 2) return n;
        else if (n == 3) return 4;

        vector<int> dp(n + 1);
        dp[1] = 1, dp[2] = 2, dp[3] = 4;

        for (int i = 4; i <= n; i++) {
            dp[i] = ((dp[i - 1] + dp[i - 2]) % 1000000007 + dp[i - 3]) % 1000000007;
        }

        return dp[n] % 1000000007;
    }
};